Question: "Do you think a viable alternative fuel source to replace petroleum will be discovered within or lifetime?" -- Good_Ol_Boy

Answer: It's impossible to know exactly what the next big technological leap forward will be, but if I had to guess, I'd say oil shale.

Israel's already using it for fuel, most estimates seem to say that it will be financially viable at $40 or less per barrel (oil is currently at $66 a barrel), and the US has enormous reserves, roughly equivalent to 5 times the size of Saudi Arabia's oil reserves.

Technologically, we seem to be fairly close to being able to use oil shale on a large scale and once we get there, it will drop our reliance on foreign sources of oil considerably.

Once that happens, my guess is that the drive for alternative fuel sources will probably slacken quite a bit, since that sort of research is generally driven by attempts to find a way to get cheaper fuel.

But still, you never know when there may be a big breakthrough and if I were guessing -- well, let's just say I have a lot of confidence in the skill of American scientists and a lot of optimism about the future, so I believe they will probably come up with something better and cheaper than oil within the next 40-50 years.